Modern reconstruction of a 16th century altitude sundial for studying its mathematics and accuracy. An altitude dial uses the height of the sun to find the time. The dial is double-sided with the two half-years back-to-back.
Erasmus Habermel was a renowned scientific instrument maker working in the court of Emperor Rudolf II in Prague in the 16th century. He made instruments for all disciplines including astronomy and navigation. One of his sundials is an altitude dial in the clocks collection of the Augustine Museum in Freiburg im Bresgau*. It is an elegant circular dial and the mathematical construction is intriguing.
Altitude sundials take many different forms, which all depend directly or indirectly on the height of the sun. The delineation of this dial appears to be a graphical projection of the sun’s position in the sky during the day and over a whole year. The precise methods will be interesting to discover, and in the meantime computer calculations have produced this modern example. The printing is on foamex plastic board and the mounting is on 3mm black acrylic. A user turns the sundial so the shadow points to the proper date, and then they read the time. It must remain vertical and the original instrument had a suspension ring at the top. The dial is for a fixed latitude.
*The attribution to Erasmus Habermel may be incorrect.